IR laser and heat-induced changes in annulus fibrosus collagen structure.

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.

Realistic three-dimensional epithelial tissue phantoms for biomedical optics.

We introduce new realistic three-dimensional tissue phantoms which can help to understand the optical properties of human epithelium as well as the optical signatures associated with the dysplasia to carcinoma sequence. The phantoms are based on a step by step multilayer reconstitution of the epithelial tissue using main components characteristic for the human epithelium. Each consecutive step is aimed to increase the similarity between real tissue and a phantom. We began by modeling the stromal layer which predominantly consists of a network of collagen bundles. Phantoms consisting of a collagen matrix alone and in the presence of embedded cervical cells were created. Their morphology and fluorescence properties were studied and were compared with those of cervical epithelium. We show that the phantoms resemble the microstructure and the optical properties of the human epithelial tissue. We also demonstrate that the proposed phantoms provide an opportunity to study changes in optical properties of different tissue components as a result of their interactions with each other or exogenous factors.

Fiber optic probe for polarized reflectance spectroscopy in vivo: design and performance.

We present the design and construction of a fiber optic probe for elastic light scattering spectroscopy in vivo with polarized excitation and polarization sensitive detection. The performance of the fiber probe is evaluated using a suspension of polystyrene spheres placed atop a diffusely scattering substrate, and it demonstrates that the size-dependent characteristics of the scatterers can be extracted in the presence of a highly diffusely scattering background using a linear combination of forward and backward Mie scattering components of the scatterers. Subsequently, Mie theory calculations are performed over a broad range of diagnostically relevant parameters of nuclei-mean diameter, size distribution, and relative refractive index-to understand how the polarized reflectance measurements with the fiber probe can be used to extract morphological information about epithelial tissue. Finally, the feasibility of in vivo measurements with the fiber optic based polarization sensitive light scattering spectroscopy is demonstrated.

Polarized reflectance spectroscopy for pre-cancer detection.

Early detection of cancer and its curable precursors remains the best way to ensure patient survival and quality of life. Thus, highly selective, sensitive and cost-effective screening and diagnostic techniques to identify curable pre-cancerous lesions are desperately needed. Precancers are characterized by increased nuclear size, increased nuclear/cytoplasmic ratio, hyperchromasia and pleomorphism, which currently can only be assessed through an invasive, painful biopsy. Here, we describe the development of a non-invasive optical technique based on polarized reflectance spectroscopy that has the potential to provide in real time diagnostically useful information for pre-cancer detection. Our results demonstrate that polarized reflectance spectroscopy can be used to selectively detect the size-dependent scattering characteristics of nuclei in vivo. We gradually progress from cell suspensions to realistic three-dimensional tissue models of epithelium, then to cervical biopsies and, finally to in vivo studies on normal volunteers and clinical patients.

Optical sectioning using a fiber probe with an angled illumination-collection geometry: evaluation in engineered tissue phantoms.

We present a fiber optic probe that combines polarized illumination and detection with an angled distal probe geometry to detect the size-dependent scattering at a specific depth within epithelium. Analysis of the scattering signal by use of Mie theory allows the extraction of scatterer size and size distribution-key parameters for precancer detection. The probe was evaluated in two tissue phantoms: polystyrene beads atop collagen gel and multiple layers of cancer cells atop collagen. We also present in vivo measurements in the oral cavity of normal volunteers. The sizes of scatterers extracted from the scattering spectra corresponded to independently measured values.